To meet the increased demand for polyetherimide, a new process was invented with a new chemistry route called the displacement polymerization process. Synthesis of polyetherimide via the displacement polymerization route generally includes imidization (e.g., U.S. Pat. No. 6,235,866), diphenolic salt synthesis (e.g., U.S. Pat. No. 4,520,204) and polymerization (U.S. Pat. No. 6,265,521), followed by the downstream activities. In a specific embodiment of the displacement polymerization process, the bisimide resulting from the reaction of 2 moles of a chloro-substituted phthalic anhydride and 1 mole of metaphenylene diamine (the adduct abbreviated ClPAMI) polymerizes with bisphenol A disodium salt (BPANa2) in the presence of a phase transfer catalyst, such as hexaethylguanidinium chloride (HEGCl). HEGCl is a well-known phase transfer catalyst to make polyetherimides. Utilization of HEGCl as a phase transfer catalyst at higher temperatures is described in U.S. Pat. No. 5,229,482.
It is desirable to improve the color quality (measured as Yellowness Index, or “YI”) of the polyetherimide made by the displacement polymerization route. High color polymer requires more pigments and dyes to meet many color specifications, and the addition of excess colorants can result in loss of other polymer physical properties. A low base polymer color is therefore desirable.
There is an ongoing, unmet need for polyetherimides made by the displacement polymerization route having improved color properties, and methods of making such chloro-substituted polyetherimides.